1. Field of the Invention
The present invention relates to the improvement of a cleaning method applied to manufacturing of a group III nitride compound semiconductor device.
The present application is based on Japanese Patent Application No. 2000-256379, which is incorporated herein by reference.
2. Description of the Related Art
When a light-emitting device which is an example of a group III nitride compound semiconductor device is to be manufactured, a light-transmissible electrode, a p-type seat electrode, and an n-type seat electrode are formed by photolithography. However, residues of a photo resist and other contaminations adhere to the surface of a wafer. It is therefore necessary to perform cleaning. Particularly, of group III nitride compound semiconductors, a p-type one has high electric resistance to be electrified easily. As a result, the contaminations are apt to be sucked thereon. If the contaminations are left as they are, not only is the light-emitting device defaced, but the adhesion of a protective film also deteriorates. In addition, if the contaminations are put between an electrode and a semiconductor layer, unevenness of light emission is produced or a driving voltage is increased to thereby cause a defect of lowering the light emission efficiency or the like.
Cleaning which is an object of the present invention is to perform ashing on organic contaminations such as resist residues and so on to thereby remove the contaminations from the wafer surface.
As a method for such cleaning, there have been known conventionally a chemical treatment method, an O2 plasma treatment method (plasma ashing), and so on.
However, when such a treatment method is to be applied to a light-emitting device constituted by a group III nitride compound semiconductor, there have been problems as follows. Chemical Treatment Method
A light-transmissible electrode which is a thin film is generally provided in a light-emitting device. This light-transmissible electrode is eroded by chemicals. In addition, aluminum for use in an n-type seat electrode (n-type contact electrode) is likewise eroded by chemicals.
O2 Plasma Treatment Method (Plasma Ashing)
In a light-emitting device using a sapphire substrate, the top layer (contact layer) thereof is formed as a p-type semiconductor layer. Since the p-type semiconductor layer has high electric resistance, the p-type semiconductor layer is electrified when plasma is generated. Because of this electrification, the crystal of the p-type semiconductor layer is damaged so that its electric properties deteriorate. In addition, metal elements of the light-transmissible electrode are oxidized in high degree so that the contact resistance between the light-transmissible electrode and the p-type semiconductor layer becomes high.
Each of the above-mentioned phenomena increases a driving voltage (Vf) of the light-emitting device or causes a short-circuit current (leakage). Therefore, such phenomena are not acceptable from the point of view of the light-emitting efficiency of the light-emitting device. Thus, if cleaning the wafer surface is promoted strongly, there is a fear that the properties of the light-emitting device itself are affected. It is therefore necessary to limit the degree of cleaning.
Further, when such a chemical treatment method is to be executed, chemical collecting equipment or chemical cleaning equipment is required. Similarly, in execution of the O2 plasma treatment method, plasma generating equipment is required. Therefore, a large scale of the manufacturing equipment is needed for each of the treatment methods. This caused an increase in the manufacturing cost of the light-emitting device.